Core bit



N. ROSS CORE an 2 s-Sheet 1 Filed Oct. 1948 INVENTOR.

gj/ ederz cj y 7455' y 2, 1950 v F. N. ROSS 2,506,388

CORE BIT Filed 0st. 20, 1948' v '2'She ets-S heet 2 v /&5 E El i.

I INVENTOR. 7729/2/25] N70515:

Patented May 2, 1950 UNI TED 1 STATE S OFFICE CORE BIT Frederick N. Ross, Detroit, Mich; assign'orto Koebel Diamond'Tool- 00., Detroit;Micli.,- a-cor notation of- Michigan Application October 20, 1948; Serial No. 55,520

9 Claims;

Thisinvention re1ates todrillbits or similar tools useful, for example; invd'rilling'into hard earth strata, such as packed or consolidated sand, rock formations, sandstone and the like. The invention is especiallyapplic'able to drilling tools commonly. known as core bits which are employed widely in'coring operations when drilling for oil or. for other purposes wherelit is desired, for example, to make soundings in order. to obtain specimens. of. earth. formations for geological analysis.

Core bits'employedin coring wells are frequently equipped. with diamonds in order to increase" the drillingrate and'pro'long the life of the bits'.' In the case of diamond core bits the diamonds are usually setin a matrix formed, for

example, of sintered powdered or comminuted metal. This matrixorslugis permanently secured as by brazing to they body of the core bit" which'in turntis threaded for attachment to the corebarreli Since the core bits are subjected to extremely hard usage; wear and shocks during,

the drilling operations; the cutting portions there of often become" fractured; chipped, broken or otherwise damaged, making it usually necessary toireplace the entire'core bit. The damaged core bit can seldom be usefully repaired after being withdrawn from thewellor hole being coredout;

Hence the bit-is usually scrapped; even though only a portion-thereof is damaged and the remainder is in--useful condition; The relatively highcost of thecore bits; especially diamond core bits; greatly increases the'cost'of drilling operations as" a result'of the necessity of scrapping the entire core bit whenever damage thereto of such nature occurs as" to-render-the bitinoper-'-- ative or inefiectual for efiicient coring work.

One of the chief" objects-of'the invention is to overcome theioregoing disadvantagesby providing a bit which is not only efiicient in carrying out the work required of it but which ma be readily repaired or renewed as to usefulness when only partially damaged'or worn'.

Another important object of the present invention'is to providea drill bit of'improved construe? tion' having cutting portions or members which maybe removed and: replaced, thereby prolong.-'

ing the life of the bit as a whole, reducing greatly the overall cost thereof, and as a consequence reducing the cost of' drilling operations.

A further" object'of the invention 'isto provide an improved "drill or core bit comprising asup'-- porting body carryingll-a number of drill inserts: or "sections which are adapted to berigid1y se-- cured in -position on the. body against: dislodge ment or dispmcementwhiie at the same time Ca? pable of being readily. removed for replacement veriticn' isto' provide afcorebit' comprising an.

annular body having radial slots or recesses for thereceptiori of drillinsertsaridmeans for firmly and'rigidly clampingfthe inserts in" position against" dislodgement" during operation, said" drill inserts and clamping'means beingpreferably removable "and 'repl'a'ceable in order to prolong the life 'of'the 'corebit.

Still another'object is to providea drill-con struction ofthecharacter described which is of simplified construction" and design; thereby achieving-optimum economy in manufacture and maintenance and permitting repair-sand replace mentof parts witha minimum of expense-and lost time.

Other objects of this invention will appear in the following description-and appended claims; reference'being had to'the-accompanying drawin'gs forming-a part of this specification wherein like reference characters designate corresponding parts in the several'views'.

Fig.11 is a fragmentary side elevation of a core bit embodying the present invention and in-- stalled on thelowe'r end of a'core barrel, a, number 'of" the cutters "and clamping devices being-- removed andthecore barreland a portion of the core bit being sh'own in vertical mid-section to illustrate the structure clearly.

Fig. 2' is a fragmentary enlarged bottom view of th'e core bit; taken in the direction of the ar-' rows substantially-along the line 22 of Fig. 1.

Fig." 3 a fragmentary vertical section taken substantially the direction of I the radical arrowsalbngthe circumferential line 3-3 of Fig-2; Fig. 4 is a fragmentaryvertical section talren substantially "along" infthe -direction' of thearr'ows the line 44=0f -Fig; 3.

Fig.5 is a fragmentary vertical sectiontaken in the direction 0f the arrows substantially along the'line-55'of,Fig. 3f

Fig. 6 is a' fragmentary bottom view'of a core bit: constructed in accordance with another em bodiment of the inventiont members being" preferably clam'l' e'dftothe body by means of devicesfwh'i'cli- Fig. 7 is an enlarged section taken substantially through lines 'l'! of Fig. 6 looking in the direction of the arrows.

Fig. 8 is an enlarged section taken substantially through lines 88 of Fig. 6 looking in the direction of the arrows.

Fig. 9 is an enlarged fragmentary inside elevation of a portion of the core bit shown in Fig. 6.

Fig. 10 is a side elevation of one of the drill inserts in the embodiment of Fig. 6.

Fig. 11 is an end elevation of the drill insert shown in Fig. 10.

Before explaining the present invention in detail it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

In the drawings there are illustrated, by way of example, two embodiments of the present invention as applied to a core bit, preferably Of the diamond type, wherein the cutting or drill elements are mounted around the lower end of an annular or tubular supporting body which in turn is mounted upon the lower end of the usual core barrel. During a drilling operation the core barrel and bit are rotated about the longitudinal axis thereof at a, suitable speed, such as between 100 R. P. M. and 150 R. P. M. The core bit cuts a generally circular hole and at the same time separates from the earth a central core which is forced upwardly through the bit and barrel as the drilling operation proceeds.

It is important that the core bit be made rugged and strong so as to enable the bit to cut the maximum possible depth before replacement becomes necessary due to wear, and further that the construction of the bit be such as to ensure the formation of an unbroken core. Heretofore, it has been the practice to secure the core bit cutting elements permanently and solidly to the body of the bit, as by brazing, thereby to assure the production of a bit having the greatest possible strength. As pointed out above, such a construction precludes repair of the bit in a great many instances where damage to the bit has been only of a partial nature. In accordance with the present invention the drill or cutting elements of the bit are made separable from the body, yet means are provided of such character as to enable the cutting elements to be so rigidly clamped or attached to the body as to render the structure in eifect substantially a solid unit having as high a degree of strength and ruggedness as heretofore.

Referring to the embodiment of the invention illustrated in Figs. 1 through 5, there is provided a core bit having an annular body 213 reduced and exteriorly threaded at its upper end 22 and adapted to be threaded into the lower tapped end of a conventional core barrel 24. As illustrated in Fig. l, the core bit is formed with an internal tapering annular wall 26 which converges toward the lower end of the bit 20. In accordance with usual practice there is mounted during use within the core bit 20 a tapered split ring known as a core catcher (not shown), which is provided with a number of internal ribs or dogs adapted to grab the core when the split ring is forced downwardly within the tapered interior wall 26 of the core bit 29. It will be understood that during the 4 coring operation the core slides freely through the core catcher ring, but when the bit 26 is pulled off bottom or drawn upwardly, the core catcher is forced down into the tapered wall 26 causing the ribs or dogs of the core catcher to tighten around the core.

The body of the core bit 28 terminates below the tapered inner wall 26 in an annular opening. The lower annular edge of the body 2!) is machined to provide a number of equally spaced transverse radially extending slots 28 for the reception of a corresponding number of drill inserts or cutting elements 36. Each insert may be formed from a matrix of sintered powdered or comminuted metal alloy having a number of protruding diamonds 31 set in the outer surface thereof in accordance with conventional practice.

Each drill insert 30 is formed in the present instance with an upper portion or head 32 having parallel outer surfacees corresponding in depth substantially to the depth of the slots 28 and dimensioned so as to fit snugly thereinto. At the base of the head portion 32, the parallel sides 34 of the insert so are recessed topro-vide the parallel shoulders 36. The cutting face 38 of each insert 3%? is generally arcuate in shape in a radial direction. Thus a cutting element or insert 39 is formed having a generally T-shaped cross section taken circumferentially with respect to the core bit 29, Fig. 3, and generally oval with parallel upper edges at the head portion 32 when the section is taken radially, Fig. 5. The upper end of each insert as is machined transversely to the radial slots 28 to provide a central rectangularly sided slot or keyway 40, Figs. 3 and 5.

Also as illustrated in Figs. 3 and 5, the body 20 is drilled vertically through the base of each slot 28 to provide a cylindrical hole 42 for the reception of the shank of a dowel pin or adjusting stud 44 which has a slip fit within the hole 42. The pin or stud 44 terminates in a hexagon head 46, Fig. 2, dimensioned to fit snugly within the slot 40 in the insert 38. Since the shank of the pin or stud 44 has a snug fit within the hole 42, it is desirable to machine an air bleed groove 48 in the length of the pin. From the foregoing it will be seen that each drill insert or cutting element St has a rectangular sided upper head portion 32 adapted to fit snugly into any one of the radial slots 28 in the body 20 and has a transverse keyway or slot 40 at its upper end within which the hexagon head 46 of the pin 44 is keyed. The slot 49 is not adapted to prevent lengthwise, i. e. circumferential movement of the head 46. However, by virtue of the fit of the head 46 within the slot 40, displacement of the drill insert 36 in a radial direction is prevented.

The several dri11 inserts 30 are rigidly held in position on the lower end of the body 2c of the core bit by means of a corresponding number of clamping devices 50, each being wedge shaped radially so as tospace the parallel sides 34 of the inserts 30 circumferentially around the core bit 25. Referring particularly to Figs. 2, 3, and

4, it will be seen that each clamp 50 has a fiat upper face 52 and plane vertical side walls 54 which diverge radially outward. Each clamp 50 terminates downward in generally arcuate edges 55, Fig. 4. Between these edges 56, the clamp 50 has a concave relief 58, extending from the inner end to the outer end, and through which is drilled a vertical hole counterbored at 62, Fig. 4. The inner or narrow end of the clamp 50 terminates in an upwardly projecting heel 84.

thetclamps 0 .are ,installed v,in position,

the heel,.- .64'aoftqeach clamp. 50 extends into ..the g roove fiii and. .abutsthe shoulder 6.8, .thus,provid .sa-means to preventdisplacement. r-tne.. 1an p 50 in an outward radial direction. .,Each-clamp ",59 is additionally secured sin position b .means pf, ascrew .ln havinga threaded shank :andtermi- .natinaat itslou'ter, end ins-head 12 adapteditc ,belreceiuedtyvithin the pounterbore .62. .The s hayk-h the screw is ,threaded. into a rtapned ,fholeldlin the body c211. Whenthe;clamps-5ll .are

-.;in sta1led,,sufiicierit ,elearanee 1.6 is .allowed obetw en th -.up er surface for l th c m I 50 nd 416. an the-:adjacentisurfaces of. ,the-b od y 3,0 0 ensure-the elampbeingrdrawn by the, screw .10 s ecurely against the overlying shoulders .36

df-theinsertsaaq, the by v i idly iloeking -:the in.-

serts 30 to the core bit and within the'Iadi-al slo s #8 vt ereof.

lt will he, notedthat. the-lower ends of the drill inserts 3.0, se F -p otrude below he lower 6 pin AA to be ,turned its the desired position of vadjustment,aiter swlglich.the .pa1';ts. -are assembled .inthe mannersho. n in.=the. .drawi-ngs.

-Referring 4-150 Fig. .3, ;.the e c centricity .of, the asymmetric head 4,46 with respectetoltheoaxis .or the shaynk. .of a the ,stud ,M is exag erated for; the sake of illustration. ,Jtisto be understood-howeever that. opposite edges ,of...the. head snare, paraalleland are spaced a distance equal to the vwidth .otthe slot 40 sons to fit snugly. int0.,th e latter, E-regardless of-theyindexed position of theheafi 46. T-he distance efromnthesaxis ofathe studl gnarginaledgesiof. the clamps-'50. :By relieving the ,iaces ,oLthese. clamps at-.58, watercourses of sub ,stantial depth ,are provided between adjacent .gglrill,insergts..30. These communicate withcorrespending wertical watercourses "l8 spaced-cir- ,sumierentially around the slower .portion of the eeuterneriphery-cfthe-core t 20, ig. 1. Thus. ,ycater .or ,other liquid pumped down through the ,.core -,barrel.2 |.and cerehi-tz osnayiflow-putwardly sthrough ;these watercourses I.8--- 58. Although ,it isusually. the practice to -pump the waterdownyardlythnough the corezbarrelei hit will be 1m- ..gierstoodw that the qr-everse may :be employed, -i. e. :the watenmay be ;f,0rce d down the outside-of the .core barrellfl and .coresbit 2-ilfand caused to flow ,through the .water courses 58-+l8 into the inside ,pf .the ordbitllo. The pressure,-:of the' water gvhen eaused ,to ,ilow in this .manner may rbe'utili zed to lift the core and thereby-permit elimination of the aforementioned core catcher.

.11 accordance with-the present invention as embodied in the structure shown in Figs. 1 thronghj, ,means are provided tfor adjusting the ,drill inserts. 3fl radially so as :toeompensate for -,wear,.oceu g during theedrilling operation. :In sqm i s ancesthe wearatake pla un n y on some ,,or all ,of the drill inserts .30 around the ,outsidepr insidaof thecore bit Y21], and where the drill inserts .are studded on their cutting :iaces with diamonds .3,l Wearing downof the .diamonds 3,! aoceursafter: aner d lei-operation. {If-his wear results in varying ,undesirably-the size -of the slot out by the tool ,andreduces the eflectiveness as wellasthe usefullifeof the tool. Hence, in ac- .cordance withthe particular embodimentof Figs. throngh 5, thekeying or interlocking connection .betweeneach ,stud 44 and its associated in- .gert 3.0 is ,suchasto permit the latter to be adjusted radiallyeither inwardly or outwardly.

IIfhejo-regoing is accomplished in thepresent in stance ,byiorm e th he agona .head 46 asymmetri al y nd .eccen c ly with respect-t t e of the shank of the .stud 44., enabling the ,5}: [d 44 to beturned to any one of six indexed gositions so as ,todispose the insert in a desired radial position with respect to the body 2,0 ,of the cor .bi Adjustment of each drill insert 30 may be accomplished by remoying the clamps .59 opposi e-sides eithe i ser then r o in perpendicularly.toieither,of the edges. oft-thehead s46 marked n -,are equal, and. obviously equal to yonerhalf the widthof v,the slot A0. Thus .the head-4'5. maybe consider-edin-.theposition otzero --,co cec ion, whencaligned as shown inFig. 2. wi th zone of :the 0,edges-adjacenh-the exterioredge-E --,of the slot 40.

Thedistance efromnthe axis :of "the, stud 44 :pertpendicularly :to the edgeof ,the ;head -46 marked -+1 is feilual :to ,one-half ;the said width --pf the slot plus --a"preselected unit of adjustment, which -may @be once-hundredth :,of.- ,an.--inch, ,fora-example. Similarly, the distance .f-rom the axis of the stud 44 perpendicularly to the .edgeof ,the- ,head 4'6-marked +2--.-isequal to one-half the .width; of the ,slot 40 plus :two-hundredths \of an inch 101 -;two of :theaaforesaid .--units -of adjustment. ,vIn ;order -.to preserve the :required ,dimensions ..be tween opposed parallel-edges of the. head 4'6, the correspondin distancesnbetweenetheaxis of the stud 44 perpend-icularly to the. edges of the head den-marked 1 and -72 @are respectively-enablin- .dredth and two-.hundred-ths ofean inch less than one-half :thewidth: of the slot 40.

Obviously, when :the head is turned so that ..either the-edge marked +2 or +1 is adjacent \the exterior slot edge .11, the insert :30 will be vmoved radially outward either -two- -hund-redths or-one-hundredthsof an inch, as the case may be, 1 from the :zero position. The insert .3 0 {is similarly moved radially inward either one or two- .hundredth of :an inch, ras the'case may :be, .by aligningthe edges marked "l-.or -.2 with the ,exterior .edge .E.

The-above dimensionsarepurely.arbitraryior the purposes :of illustration. Likewise, it is apparent that polygonal headslsimilar ,to the head -46 but having more orwless than six sides and {other degrees of eccentricity or asymmetry than :described herein will be employed where desired 'FtO effect other degrees oi adjustment of the inserts 30. Also, where desired, the .numbers 0, 1,-etc., or other-suitableidentifying indicia maybe markedqon theproper edges of the ,head :46. From the foregoing it will be seen that the drill inserts .30 may be adjusted :radially either .outwardly -or inwardly in order :to compensate for .wear. For example, assuming that the outer surfaces of the inserts have been worn down approximately .02 of an inch and the inner sur- :faces .have been worn approximately .01 of :inch, alternate drill inserts may be adjusted'outwardly .02 of an-i-nch each and the other alter, ynate drill inserts may be adjusted inwardly 401 :of an inch each. This will enable the core. bit to continue tocut the same size slot since alternate drill inserts willcut-on the outside and theremaining drill inserts 'will cut on the inside. It will be apparent that other suitable adjustments- ;may be made to compensate for wear on -individual drill inserts, thus prolonging the useful. life of the core bit.

the inse t as to p rmi t e stud ridowl :75; wi h. the arm inserts an. ri idly clamped ing shoulders 35 of the inserts 30, as effected upon tightening the screws I0, securely holds the inserts 30 upward in position against the bases of their corresponding slots 28. Engagement of 'the heel E4 on each clamp 50 with the abutment shoulder 68 prevents outward radial displacement of the clamp 50, thus relieving the shear load on the screw I0. Displacement of the drill insert 38 in either radial direction is blocked by means of the head at keyed within the slot 40.

In the embodiment of the invention illustrated in Figs. 6 to 11 inclusive, the tubular body 80 of the core bit is similar to that illustrated in Fig. l, with the exception of the provision for mounting and clamping the drill inserts 82 in position. Rigidly secured to the body 80 around the lower inner side thereof is a continuous ring 84 which may be fixed to the body 88 as by welding at 86. Abutting the outer periphery of the ring 84 and the lower edge of the body 80 is preferably a detachable annular spacer ring Bl having the lower edge thereof machined at equally spaced intervals to provide radial slots 88.

Each drill insert or element 82 is generally T-shaped as shown in Figs. 9 and 11 and, accordingly, is provided with a rectangular sided head 90 adapted to fit snugly within a slot 88 with the remainder of the drill insert 82 projecting downwardly below the lower edge of the core bit body 80. The drill insert 82 is assembled by sliding the head 98 in an inward direction into the slot 88 until the head 98 abuts against the fixed stop ring 84. A clamp 92, wedge shaped similarly to the clamps 50, fits snugly between each adjacent pair of drill inserts 82 and, as shown in Fig. 9, underlaps the projecting portions 94 of the adjacent drill insert heads 90. Each clamp 92 is rigidly secured to the body 80 by means of a screw 86 passing vertically through the screw holes 88 and I80 provided therefor in the clamp 92 and ring 87 respectively and screwing into the tapped screw hole I02 within the lower end of the core bit 80. Tightening of the screws 85 draws the clamps 92 tightly toward the body and th annular spacer 8?. The head I04 of each screw 98 is countersunk in the end of the clamp 92 as shown in Fig. 8. When the clamp 92 is drawn up tightly toward the core bit 80 and against the projecting portions 9d of the adjacent drill inserts 82, it will underlap the lower edge of the inner fixed ring 84 and will rigidly hold the inserts 82 against downward displacement during operation. After the inserts 82 and clamps 92 have been installed, an outer ring I06 is slipped downwardly over the core bit body 80 into abutting engagement with the clamps 92 and drill inserts 82. Thereafter, the outer ring I06 is shrunk onto the body 80 tightly in position, with the spacer 81 and head 90 interposed between the rings 84 and I06.

The length of each head 95 is selected so that the latter will fit snugly between the rings 84 and I06 Without radial play. Accordingly, the overlapping of the heads 93 by the inner clamping ring, which is welded to the body 80, prevents 'tioned and shrunk onto the body 80.

displacement of the inserts 82 radially inward; Since the outer shrunk-on clamping ring I08 overlaps the outer sides of the heads 90, it will prevent radial displacement outwardly of the drill inserts 82. The vertical thickness of each head 90 is selected so that the latter will be securely clamped against vertical play or movement between the clamps 92 and the base of the slot 88 within which it fits.

The interlocking keying engagement 'of the head 90 with the clamps 92 will prevent displacement of the drill inserts B2 in a downward direction. The drill inserts p82 protrude a suitable distance beyond the lower ends of the clamps 92 and are studded with diamonds I08 at their outer convex faces. Although only three protruding diamonds I08 are shown, it will be understood that this is merely for illustration since, as also in the case of the inserts 30 above described, a large number of diamonds are ordinarily set in the face of each drill insert to provide the required cutting surface.

For the purpose of repairing the core bit by the replacement of any one or more of the drill inserts 82, it will be understood that this ma be easily accomplished by sawing the ring I06 in two for the purpose of removing the same in order to permit removal of the drill inserts 02. After new inserts 82 have been installed on the core bit body 80, a new outside retaining ring I08 is posi- In the embodiment shown, the spacer ring 8'! is separable from the core bit 80, permitting economies in the manufacture of the core bit assembly and the adaptation thereof for use with drill inserts 82 of different sizes. Thus, a, drill insert having a head corresponding to the head 90, but of a different width or thickness, may be substituted for use with the core bit upon substituting a spacer ring 81 having machined slots 88 of a proper size for snugly receiving the head of the substituted drill insert. However, it is apparent that the ring 87 may be integral with the body '80 where desired.

I claim:

I 1. A drill bit comprising an annular body having a series of radial slots at one end thereof, a corresponding series of drill members having their inner ends fitting into said slots and their outer ends protruding from the body, clamping members interposed between said drill members and removably secured to the body, overlapping shoulder portions on said members for resisting axial displacement of said drill members, and connecting means between the inner ends of said drill members and body for restraining radial displacement of said drill members.

2. A drill bit comprising an annular body having a series of radial slots at one end thereof, a corresponding series of drill members having their inner ends fitting into said slots and their outer ends protruding from the body, clamping mem bers interposed between said drill members. and removably secured to the body, abutment means for holding said clamping members against'outward radial displacement, said drill members and clamping members having overlapping shoulder portions to restrain axial displacement of said drill members, and means for keying the inner ends of said drill members to the body to restrain radial displacement thereof.

3. A core bit comprising a tubular body, a series of annularly spaced radially extending drill ele-' ments mounted on one end of the body, wedge shaped clamping members interposed between said elements and each having radially inwardly converging sides engaging adjacent sides of a pair of elements, each element and an adjacent pair of said members having interengaging shoulder portions to prevent relative axial displacement, means for securing said members to the body to effect binding engagement between said interengaging shoulder portions, abutting means between said members and body to restrain radial displacement of said members, and cooperating means between said elements and body to restrain radial displacement of said elements.

4. In a core bit, the combination of a tubular body, a series of annularly spaced drill elements removably mounted on one end of the body, a circumferentially extending slot in each of said drill elements, means for detachably securing said drill elements in adjusted positions on said body, and adjusting means for selectively adjusting said drill elements radially with respect to the body and comprising a plurality of pins rotatably mounted on the body, each pin having a polygonal head projecting into one of each of said slots, the edges of said polygonal head being arranged in equally spaced parallel pairs adapted to fit snugly within said slot and being disposed varying distances from the axis of said rotatable pin.

5. In a core bit having a tubular body and a plurality of radial slots in one end of the body, a plurality of drill elements adapted to be secured in adjusted positions within said radial slots, a circumferentially extending slot in each of said drill elements, holding means for said drill elements and adjustable to vary radially the operative positions of said drill elements within said radial slots and comprising a plurality of pins rotatably mounted on the body, each pin having a polygonal head projecting into one of each of said circumferential slots, the edges of each polygonal head being arranged in equally spaced parallel pairs adapted to fit snugly within the circumferential slot therefor and being disposed varying distances from the axis of said rotatable pins, and means for securing said drill elements in their adjusted positions within said slots.

6. In an annular core bit having a series of annularly spaced drill elements removably mounted on one end thereof, means for selectively adjusting said drill elements radially with respect to the core bit and comprising I3, plurality of polygonal adjusting heads rotatably mounted on said core bit, the edges of each polygonal head being disposed varying distances from the axis of rotation of the head and each head being disposed for selectively presenting its edges in abutting relation with one of each of said drill elements so as to vary the radial position thereof with respect to said axis, and means for securing said drill elements in their adjusted positions on said core bit.

7. In a core bit having a tubular body and a plurality of radial slots in one end of the body, a plurality of drill elements adapted to be se cured in adjusted positions within said radial slots, adjustable means to vary radially the 0perative positions of said drill elements within said radial slots and comprising a plurality of polygonal heads rotatably mounted on the body, the edges of each polygonal head being disposed varying distances from the axis of rotation of the head and each head being disposed for selectively presenting its edges in abutting relation with one of each of said drill elements so as tovary the radial position thereof within the slot therefor, and means for securing said drill elements in their adjusted positions within said slots.

8. A core bit having a tubular body and a plurality of annularly spaced radial slots in one end thereof, a plurality of drill members, each having a head adapted to be removably inserted into a recess and to be snugly retained between the circuferential walls thereof against circumferential movement, inner and outer annular rings secured to said body and disposed across the inner and outer ends respectively of said radial slots, said heads being adapted to fit snugly within said slots between said inner and outer rings, at least one of said rings being removable from said body to facilitate removal of said drill members from said body, and axial clamping means for removably clamping said drill members within said slots against axial displacement.

9. In a core b-it having an annular body, the combination 'of a concentric annular ring separable from said body and having one face abutting said body at one end thereof and having a plurality of radial slots:- in the other face, drill members having portions insertable into said slots and detachably anchored therein against circumferential displacement relative to said ring, means for holding said ring and drill members inv said slots against radial displacement, means securing said ring against circumferential displacement relative to said body, and clamping means cooperable with said last named securing means for removably clamping said drill elements and ring against axial displacement relative to said body.

FREDERICK N. ROSS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

